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1. Which compound has a nonpolar bond in which the electrons are shared equally?

• A. H₂O
• B. NH₃
• C. Cl₂
• D. CH₄

Correct answer: D

Rationale: The compound CH₄, methane, has a nonpolar bond where carbon and hydrogen share electrons equally. This occurs because carbon and hydrogen have similar electronegativities, meaning they have equal abilities to attract shared electrons. Consequently, a nonpolar covalent bond is formed due to the balanced sharing of electrons between these atoms. Choices A, B, and C do not have nonpolar bonds with electrons shared equally. In H₂O (water), there are polar covalent bonds due to the difference in electronegativity between hydrogen and oxygen. In NH₃ (ammonia), the nitrogen-hydrogen bonds are polar because of the electronegativity difference. In Cl₂ (chlorine gas), the Cl-Cl bond is nonpolar, but the question specifies a compound, not an element, and chlorine does not share its electrons equally with another element in a compound.

2. What does the sum of protons and neutrons in an element represent?

• A. Atomic number
• B. Mass number
• C. Atomic mass
• D. Neutron number

Correct answer: B

Rationale: The sum of protons and neutrons in an element is known as the mass number. The mass number is an important concept in chemistry as it represents the total number of nucleons (protons and neutrons) in an atom's nucleus. It is different from the atomic number, which represents the number of protons in an atom. The atomic mass is the average mass of an element's isotopes, taking into account the abundance of each isotope. Neutron number, on the other hand, specifically refers to the number of neutrons in an atom's nucleus. Therefore, the correct answer is B, mass number.

3. What type of bond is present in sodium chloride?

• A. Covalent
• B. Ionic
• C. Metallic
• D. Hydrogen

Correct answer: B

Rationale: Ionic bonds are found in sodium chloride. In an ionic bond, one atom donates an electron to another atom, resulting in the formation of positively and negatively charged ions that are held together by electrostatic forces of attraction. Sodium chloride is a classic example of an ionic compound, where sodium (Na) donates an electron to chlorine (Cl), forming Na+ and Cl- ions that are attracted to each other, creating a crystal lattice structure. Covalent bonds involve the sharing of electron pairs between atoms, which is not the case in sodium chloride. Metallic bonds occur in metals where electrons are delocalized and shared across a lattice, unlike the specific transfer seen in ionic bonds. Hydrogen bonds are a type of intermolecular force, not the primary bond type present in sodium chloride.

4. What is the charge of noble gases?

• A. -1
• B. 0
• C. 1
• D. 2

Correct answer: B

Rationale: The correct answer is B: 0. Noble gases have a charge of 0 because they have full valence shells and are inert. This makes them stable and unreactive, resulting in a charge of 0 as they do not readily gain or lose electrons. Choices A, C, and D are incorrect because noble gases do not typically form ions by gaining or losing electrons, so they do not carry a charge of -1, 1, or 2.

5. Which branch of chemistry deals with the quantities and numeric relationships between compounds in a chemical reaction?

• A. Stoichiometry
• B. Molecular chemistry
• C. Atomic chemistry
• D. Thermodynamics

Correct answer: A

Rationale: Stoichiometry is the branch of chemistry that deals with the quantitative relationships between reactants and products in chemical reactions. It involves the calculation of quantities of substances consumed and produced in a chemical reaction based on the balanced chemical equation. Choice B, 'Molecular chemistry,' is incorrect as it focuses on the structure, properties, and reactions of molecules. Choice C, 'Atomic chemistry,' is incorrect as it primarily deals with the study of atoms and their interactions. Choice D, 'Thermodynamics,' is incorrect as it pertains to the study of energy and heat transfer in chemical and physical processes.

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